Zb.gozdarstva in lesarstva, L.20, št.l s. 69 - 76, Ljubljana 1982 
Oxf. 425.1:176.1 Fopulus spp. 
THE INFLUENCE OF OZONE ON THE GROWTH OP SOME POPLAR SPECIES 
J.MOOI, dipl.inž. 
Research Institute far Plant Protect.ion 
Binnenhaven 12, Wageningen, 
The Netherlands 
69 
VSEBINA 
1 n troduct ion 71 
2 o
3 
Concentrations in the Nederlands 72 
3 Material s and methods 72 
4 Symptoms 73 
5 Resul ts 73 
6 Discussion 74 
7 Literature 75 
70 
1 NTRODUCT ION 
From 1 iterature it is known that Populus tremuloides is one of the mo"st sensi-
tive species to so2 and o3 (Karnosky, 1976) and a more than additive effect 
exists when these gases are appl ied in combinati.on during three hours. Kohut, 
a.o. (1976) have carried out fumigations on Populus maximowiczi i x trichocarpa 
(clone 388) with relative high concentrations. of o
3 
and PAN. It seemed that PAN 
did not give symptoms, but o
3 
did. A combination of these gases caused an addi-
tive or synergistic effect, The symptoms produced in their exposures look like 
a dark brown bifacial necrosis. Davis and Wood (1972) have fumigated eighteen 
species of conifers beginning 4 weeks after needle emergence with a concentra-
tion of 500 ug o
3
;m3 during eight hours. It seemed that nine species were more 
or less sensitive; e.g. Larix decidua, Pinus nigra var. nigra, Pinus sylvestris 
and Pinus strobus. Species without symptoms were e.g. Pseudotsuga menziesii and 
Picea abies. Within populations of o
3 
sensitive species there was a great dif-
ference in the sensitivity of individual plants. Although the given concentra-
tions were rather high, it may not be excluded that also in the Netherlands the 
same concentrations could be measured during short times. Almost all fumigation 
experiments mentioned in literature are of very short tirne, some hours till at 
most some days. So it is very difficult to relate these results to practical 
circumstances. Fumigation experiments on Populus species, carried out .at the 
1.P.O. in the years from 1973 till 1976, showed that there is an early leaf-
drop as result of a fumigation with low concentrations of o
3
. The plants were 
fumigated 12 hours a day with a concentration of 100 - 120 ug o
3
;m3 during 5 
months. lf this leafdrop could also be observed for many Populus species it 
might be acceptable that the leafdrop which has been seen in practice was not 
only caused by drought but also by the relative high concentrations of o
3 
du-
ring the vegetation period. Ambient air measurements of o
3 
showed that concen-
trations of 100 ug o3;m
3 frequently occur. The precursors for o
3 
(e.g. NOx and 
C H ) are mainly produced in industrial areas and cities, while other pollutants 
X y 
are present to reduce the o
3 
concentrations (e.g. NO, dust and soot), the so 
called sink for o
3
. lf by wind action precursors of o
3 
are blown outside an ur-
ban area, the o
3 
concentration will increase in the air because no reaction with 
71 
other air pol lutants is possible. This explains why o
3 
injury can be found 
many tens of kilometers from large cities or industrial areas. Concentrations 
even till 500 ug o
3
;m3 were measured- (Georgii, 1977, Guicherit, 1975). 
Because of early leafdro_p it is very interesting to see if yield reduction 
co-uld also be produced by low levels of 03" For thls reason some _artif1cial 
fumigations were ca-rried out on some clones of Populus x eur_americana {delto-
ides x nigra). These clones are Heidemij, Spijk, Zeeland and Dorskamp. 
OJ - CONCENTRAT JONS l N THE NETHE-RLANDS 
The concent~ations used in the fumigation experiments _are based on those found 
in ambient ai r in the Netherlan<ls. In table i the o
3
-concentrations during the 
vegetation period on four places in the-Ne~herlands are given. 
Table 1. o
3
-concentra·tions (ug/m3) at some places in the Netherlands du-ring 
the period 1-4-1976 til! 1-10-1976 (hourly averages). 
Eindhoven Maassluis Schiedam Hoogvl iet 
da i I y average 70 40 37 60 
from 1 /4-1 /1 O 
50 percent i le * 60 28 30 45 
75 percentile ··- 98 54 31 b6 
98 J:)ercent i le -;': 200 138 116 162 
max.hourly average 324 350 250 307 
1, - percentile = % of the number of measurements is below the given value. 
MATERIAL$ AND METHODS 
The trees were potted in vessels ot 27 litre which were provided with an auto-
matic water supply system. Fifty cuttings of each cv. were placed in a mixtu-
re of peat and 15% riversand. rrom February til l September a manuring of 1 g 
12-10-18 per litre soil was given every month. The plants were fumigated in 
longterm fumigation greenhouses (area 12 m2), cubic capacity 30 m3, air change 
capacity of 80 m3/min. By means of a cooling machine it was possible to regu-
late temperature and more or less the relative humidity (R.H.). Dependent on 
outside conditions the average temperature was 16°c, the R.H. 63% and the l ight 
72 
intensity 65 W/m2 . Because of differences in climate conditions between the 
fumigation greenhouse, the trees were changed every three weeks from fumigation 
greenhouse. Possible effects of differences in climat& conditions on the re-
sults of the experiments were eliminated in this way. 
To maintain the desired concentration the ventilated air was filtered by acti-
ve charcoal. To this purified air a known quantity of o
3 
was added by means of 
an ozone-generator (Fischer). o
3
- concentrations were measured by means of che-
moluminescence (Me. Millan 1100-3B). The monitor was calibrated with a buffered 
solution of potassium jodide. 
In this paper only the results of the last of three experiments will be repor-
ted. The trees were fumigated every day from 8.00 a.m. till 8.00 p.m; with an 
average concentration of 81 ug o
3
;m3 (s=22). This concentration is a little·bit 
higher than those found in the Netherlands. 
SYMPTOMS 
After about 10 days of fumigation a very sl ight chlorosis was seen on the upper 
leaf surface. This slight chlorosis sometimes changed afterwards in a very 
slight necrosis. The recognition of o3- symptoms in practice is very difficult, 
because similar symptoms may also be produced by nutrient diseases (N-, K-, 
Mg-deficiency), virus diseases, insects, herbicides, etc. It is necessary to 
compare with untreated plants. After about six weeks of fumigation the first 
leafdrop was seen. 
RESULTS 
The plants were harvested on October 13, 1977, although the vegetation period 
was not completely at the end. The dry weight of the leaves which were drop-
ped and those which were at the stems and dry weight of the stems were deter-
mined. The most important result from this fumigation is the fact taht low le-
vels of o
3 
can produce a heavy leafdrop at cvs of Populus x euramericana (ta-
ble 2). A reduction of total dry matter production (0-6%) and of total dry mat-
ter production of the stems (4-12%) was found if compared with the control 
plants. The number of leaves at the stems varied from 36% till 45% as compared 
73 
to the control plants. Cv.Zeeland has a lower (ca. 25%) total dry matter pro-
duction than cv. Dorskamp, however there is no great difference between the 
clones in dry matler production of the stems (8%) and the leaves at the stems 
(4%). Cv. Dorskamp has about two times more leafdrop than cv. Zeeland if com-
pared as a percentage of the dry matter production of the control. 
DISCUSSION 
In not polluted areas o
3
-concentrations from 80 - 130 ug o
3
;m3 may occur, which 
may have a natura] base. These concentrations were measured during short pe-
riods, so the annual average of natura] o
3 
is much lower. o
3
-concentrations as 
used in the fumigations frequently occured in the Netherlands. The most impor-
tant result of this investigation is the fact that low levels of o
3 
can produ-
ce a heavy leafdrop at some cvs of Populus x euramericana (seven till thirteen 
times more than the control plants). Also a reduction of dry matter production 
of the stems was observed (4-12%). Because of other fumigation experiments this 
fumigation must be stopped, so the trees were not completely at the end of their 
vegetation period. This is the reason why the difference in dry matter produc-
tion of the stems were rather small, 
The next results are not only based on data given in table 2, but also from 
earl ier fumigation experiments. A maximum reduction of dry matter production 
of the branches of 38% was found with cv. Spijk. Dependent on the tirne of fumi-
gation the fumigated plants had 10 till 56% o~ the number of leaves at the stems 
if compared with the control plants. Great differences between the used cvs ha-
ve not been establ ished (max. 9%). Except far cv. Zeeland in the last experi-
ment the average length of the fumigated branches were longer ghan those of the 
control plants. The total dry matter production (leaves + stems) of the plants 
which were fumigated til] the end of the vegetation period was 18% lower than 
that of the control plants. In fumi'gation experiments which were not carried 
out up to the end of the vegetation period, the total drymatter production was 
6,4% lower till 6,6% higher than those of the control plants. The National Mo-
nitoring Network far Air Pollution in the Netherlands has shown great differen-
ces in injury on tobacco Bel w3 at di fferent places in the Netherlands (floor, 
Posthumus, 1977). So, it may be acceptable that the leafdrop which was seen in 
practice could be caused by 10\1 level s of 03' 
·74 
LITERATURE 
Davis, O.O. and F.A. Wood: The relative susceptibility of eighteen coniferous 
species to Ozone. Fytopathology, Vol.62, jan.1972, p.14-19. 
Floor, H. and A.C.Posthumus: Biologische Erfassung von Ozon- und PAN-lmmissio-
nen in _den Niederlanden in 1973, 1974 und 1975. v.-0.1. - Berichte nr. 270, 
1977. 
Georgii, H.W. u.a.: Bildung und Transport von Photooxidantien im Raum Bonn-
Koln und Frankfurt/M. V.O. i.Berichte nr.270, p.19-24. 
Guicherit, R.: Fotochemische smogvorming in Nederland. Rapport G 646, 1975, 
lnstituut voor Milieuhygiene en Gezondheidstechniek T.N.O. te Delft. 
Karnosky, D.F.: Threshold levels for foliar injury to Populus tremuloides by 
sulfur dioxide and ozone. Canadian Journal of Forest Research 6 (1976): 
166-169. 
Kohut, R.J., Davis, D.D. and W. Merrill: Response of Hybrid Poplar to simulta-
neous exposure to ozone and PAN. Plant Disease Reporter Vol. 60, nr.9, 
1976, p.777-780. 
75